Metal halide lamps generally include a relatively centrally located arc tube situated within the confines of an outer glass bulb. These arc tubes are conventionally made of quartz and operate at extremely high temperatures and relatively high pressures. Under certain undesirable conditions, a system failure or internal factors will result in a safety hazard being created, whereby a violent shattering of the arc tube will send hot glass and lamp particles into contact with the bulb glass which, in turn, will break, releasing the hot glass and lamp particles into the surrounding environment. Under such conditions, there is an obvious risk of severe personal injury, fire and/or property damage.
For these reasons, conventional metal halide lamps are generally supported within “enclosed” fixtures whose structure is designed to contain violently released hot glass and lamps particles. In addition, significant reductions in such potential violent failures can be achieved by replacing the lamp before the rated end of the life for the lamp. Another conventional manner for reducing the risk in which such potential violent failures includes the user's periodically turning off the lamp to permit its cooling, so that upon relighting, a non-violent or less violent lamp failure is facilitated.
As disclosed in U.S. Pat. Nos. 5,698,935 and 5,874,800, manufacturers of metal halide lamps are selling lamps for use in what are referred to as “open” fixtures. In open fixtures, the lamp is mounted such that it is exposed during its use. In order to reduce or eliminate the risks associated with violent lamp failures in non-enclosed environments, metal halide lamps may include a relatively thick shroud of quartz situated intermediate the arc tube and the outer bulb glass such that, in the event of a violent lamp failure of the type described above, the shroud is capable of containing the hot glass and lamp particles, which would otherwise impact and possibly break the bulb glass. One result is a less expensive and equally safe lamp and fixture combination suitable for indoor commercial lighting applications such as offices and retail spaces, as well as other environments.
However, to prevent the use of lamps intended to be used in an “enclosed” fixture in an “open” fixture, the newer “shrouded” lamp is provided with a different type of base so that the lamps intended for an “open” fixture can be rapidly identified and separated from lamps that must be used in an “enclosed” fixture.
Prior art lamp holders generally utilize a metal sleeve and a cantilever mounted contact to supply power to the lamp, as detailed in U.S. Pat. Nos. 5,698,935 and 5,874,800. There are many problems associated with a cantilever mounted contact and lamp interface. For example, the center contact spring may be easily displaced during the re-lamp process, the center contact spring may be displaced or dislodged if the center contact becomes bent during the re-lamping process. A cantilever mounted contact may allow a user to tamper with the center contact. For example, the cantilever mounted center contact may be bent to extend to a point above the bulb security well (or hub) so that an “enclosed” fixture bulb can be used in a lamp holder designed for an “open” fixture mental halide bulb.
Thus, there is a strong need for a lamp holder (or lamp socket) that overcomes the deficiencies of the prior art.